Signaling system



April 25, 1950 D. .MITCHELL SIGNALING SYSTEM 2 Sheets-Sheet l Filed July 25, 1945 /NVEA/TOR a M/ TCHELL ATTORNEY D. MITCHELL SIGNALING SYSTEM April 25, 1950 2 SheetsSheet 2 Filed July 23, 1945 /Nl/E/vron D. M/TCHELL By Cin@ ATTORNEY Patented Apr. 25, 1956 SIGNALING SYSTEM Doren Mitchell, Martinsville, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application July 23, 1945, Serial No. 606,658

4 Claims.

This invention relatesto selective signaling systems and particularly to selective signaling in automatic and semi-automatic telephone systems.

` Objects of the invention are an increase in the efficiency, speed and reliability oi selective signaling systems.

This invention is a selective signaling system and a method of signaling in which each of a plurality of different selective signals is transmitted by the same number of successive signal impulses, the duration of each of which may be any one of a plurality of predetermined intervals of time depending upon lthe particular 4signal being transmitted.

A feature is a signaling system in which each of a plurality of different signals consists of a particular number of successive signal impulses and in which each of said signals differs from the others in the duration of one or more of its impulses, and in which means is provided for preventing a signal indication responsive to a succession of impulses differing in number from said particular number.

, A further feature of the invention is a signaling system in which each of a plurality of different signals is transmitted by two successivesignal impulses, the duration of each of which may be any one-of a plurality of predetermined intervals of time sothat each signal is represented by a different impulse duration code.

A further feature of the invention is a signaling system in which each of ten signals corresponding to the digits 1 to 0 is transmitted by two successive signal impulses, the duration of one of which may be equal to any one of ve different predetermined intervals of time and the duration of the other of which may be equal to any onn of four of said ve intervals, the two impulses representing each digit differing from the two impulses representing any other digit in the duration of one or both of the impulses. The drawing which forms a part of this specification discloses a portion of an automatic telephone system in which the invention and its features are embodied. The invention is however not limited in its application vto the particular system and larrangement shown but is generally applicable to selective signaling.

In the drawing, Fig. 1 discloses a telephone subscribers station A including a signal transmitter SIT connected by a line Ll to a central The subscribers telephone set is of the usual common battery type. The signal transmitter is shown as including live impulse transmitting contacts Il, I2, I3, Ill and I5 and an off-normal contact ON which short-circuits the impulse contacts except during the transmission of the impulses for each code or numerical digit. Each of the transmitting contacts is opened, when actuated, for a different interval of time. For instance, contact Ii may be opened for .002 second, contact I2 for .004 second, contact I3 for .008 second, contact I4 for .016 second, and contact I5 for .032 second. vThe duration of the opening of the various contacts is arranged in a geometric progression instead of in an arithmetical progression so that percentage variations in duration are less likely to cause errors. The interval which separates the two impulses of a signal may be about .015 second and the interval which occurs between digits will be about .2 second. The signal transmitter for opening the. transmitting contact Il, I2, I3, Iii and I5 may be similar to that` disclosed in the patent to R. F. Mallina No. 2,315,344, granted March 30, 1943, each reed being designed l.to give the desired time of vibration during which the associated contact will be opened. The two reeds which are operated by each digit lever will be actuated in succession instead of simultaneously as in the Mallina patent. Alternatively, the signal transmitter may be similar to that disclosed in the patent to J. G. Roberts and C. D. Richard No. 2,246,698, granted June 24, 1941, which transmitter is arranged to transmit two impulses for each digit, each impulse being any one of a plurality of different lengths. With such a signal transmitter the ve contacts Il, I2, I3, I4 and I5 in series will be replaced by a single interrupter contact which is opened twice for each digit.

The signal code is as follows:

Length of Impulse in mil Length of Impulse in mil seconds seconds lst Im- 2nd Imlst Im- 2nd Im mgm pulse pulse Diglt pulse pulse If an additional transmitting contact is provided, the code may be expanded to fifteen signals; or, if the signal transmitting and receiving means are modified, fifteen signals may be obtained by including signals for which the two impulses are of equal duration.

The line circuit LCI comprises the usual line and cut-off relays which are effective responsive to the initiation of a call at the associated subscribers station to start a line nder or operate a line switch to connect the line to a first selector or district circuit. As shown in the drawing, the line Ll is connected through a district circuit ii to a primary switch H on a district link frame. The resistances I3 and lf3, connected in series with the repeating coil and central ofcc battery BI, enable the connection of the input conductor i5 of the signal receiving part of the register sender to the district without unbalancing the line. The longer impulses represent such low frequencies that they would in effect be partially shunted out by the repeating coil if the impulse receiving circuit was connected directly to one side of the line; but by connecting the impulse receiving circuit to resistor i3, as shown, the most favorable ratio of impulse signal to speechis obtained. The resistance I6 ma-y be provided for connection as a line termination to improve the signal shaping on long lines.

The district le and register sender in general similar in function and operation to districts and senders disclosed and described in detail in the patents to Carpenter 2,089,921, granted August 10, 1937, and 2,235,893, granted March le, 1941.

The signal receiving means provided in the register sender comprises amplifier tubes 2t, 2e and 35, a relay 39; time identifying tubes (il, ft2, 43, lili and 45 and time identifying relays El, 63, 66 and $5; The signal receiver further includes circuit means comprising relays 92, da?, Sli and S5 for translating the received impulse combinations into digitV signals. The electromagnets numbered l to t' represent intermediate signa-l relays which successively respond to each digit signal and in turn effect the operation of the various digit registers (not shown) in any desired knownk manner.

Assume that the line Lt has been connected to the district it responsive to the initiation oi a call at the subscribers station A and that a sender RS has been associated with the district i'i, whereupon diai tone i's transmitted to the subscriber in usual and well-known manner.

The calling subscriber then actuates the signal transmitter ST to transmit the office code and numerical digits of the directory number or the subscribers station` with which a conversational connection isl desired'. The circuit for trans-'- drop through resistor I3; and the grid of tube 2S isznormally negative with respect tothe cathode but'not necessarily sufiiciently so to entirely prew vent cathode-anode current. When one of the signal transmitting contacts is opened to trans'- mit a digit signal, the voltage dropin resistor 5 3 becomes Zero and therefore the grid of tube 725i goes to the saine voltage as the cathode thus causing a surge of current in the cathode-anode 4 circuit. The resistor 2l and condenser 22 introduce a degree oi filtering to aid in discriminating against voice currents. The increased current through resistor 233 reduces the charge on each of condensers 2li and 33, thus introducing a voltage drop through each of resistors 25 and so that the grid of each of tubes and 35 becomes more negative with respect to its cathode. Normally there is no difference of potential between the grid and cathode of tube 2t; whereas the grid of tube 35 is normally biased by the voltage drop through resistor 3c. Thus, the surge of current in the anode-cathode circuit of tube 2t at the beginning of a signal impulse from station A causes a reduction in the cathodeanode current of tube 26; but, since tube 35 is normally biased to cutoff, there is no elfect on relay 3S at the start of a signal impulse. The time constants of the circuit including resistor 23, condenser 24 and resistor 25 are such that the signal impulses of from .002 to .O32 second in length are satisiactorily reproduced in the cathode-anode circuit or" tube 2t.` The aforementioned decrease in the anode-cathode current oi tube 2S reduces the voltage drop through re sistor 28 so that the voltage applied across condenser 29 tends to increase.- The time constants of resistor` 23 and condenser 29 are such that the change is proportionalto': the length of the signal impulse. A limiting acti-on is obtained in tubes 2t and E6 so that the amplitude oi the impulses through resistor 2'? isr independcntof their amplitude at the grid of tube 26. As the vol-tage across condenser 29 increases, the voltage drop through resistor 3i increases' due to current charging condenser 30, so that conductor 32- and the grid of each of time identifying tubes 4i, 21E, 43, ifi and 65, become more positive with respect to their cathodes. The time consta-nts of condenser 36' and resistor 3"i are made suincient'ly long so that voltage changes across condenser 29 are repeated on the grids oiv the time identi/tying tubes. The difference in potential between the cathode-s' and anodes of these tubes is controlled by' a potentiometer comprising resistors Ml, 41X, 8, 49'- and whereby' the voltage a-p'piied to' conductor' 3'2 duc to a signal impulse of .002 second in length causes' a cathode-anode current' in tube lill' sufficient to operate the time identifying relay "5;V whereby the voltage applied to conductor 32 due toan impulse of .Oilasecondv in length causes a catl'iodeanode current in tube 4-2' s'uicifent tot operate the time identifying relay 632; whereby the voltage applied to conductor T2 due toan impulse'of .003 second in length causes a cathode-anode current in tube 'i3 suiiicient to operate the time id'er'itify-A ing' relay 63 whereby the voltage applied to con# ductOr 32' due to an impulse of .01:6 second in length causes a cathode-anode current in tube 4Q sumcient to operate the timeiden'tifying relay' 621'; and wherebythe'vvoltage applied'to conductor 32 due to an impulse er' .032 second in length causes a cathode-anode current in'l tube' 45' suffi? cient to operate: the time' identifying relay` S5'.

Thus relays El to E55V are operated successivelyV by' a signal impulse, the last one=of` the relays to be operated indicating the length of the received signal impulse. discharge rapidly through their respective tube circuits but mustv be charged through their as'-r sociated time identifying relaysthereby insuringA tube is of' short duration.

At the end of each signal impulse" transmitted Condensersiil, 52, 53", 512 and 553 from station A, the grid of tube again becomes negative with respect to the cathode so as to decrease the cathode-anode current of tube 29. increase the anode-cathode current of tu-be 2B, and terminate the cathode-anode current in the time identifying tubes. The aforementioned decrease in the cathode-anode current of tube 29, when the signal impulse ends, causes the grid of tube -to become more positive with respect to the cathode so that there will be a surge of current in the cathode-anode circuit of tube 39 suflicient to effect the operation of relay 39. The operation of relay 39 connects ground to conductor 49 to effect the operation of one of the translating relays 9i to 95, the operative energzation oi the time identifying relays being continued by current charging the associated one or ones of condensers 5i, 52, 53, 54 and 55 after the cathode-anode current is ended in the associated time identifying tube; so that the operation of relay 39 connects ground through conductor 49 and the operated one or ones of relays 6I, 62, 53, Bd and 65 to cause the operation of the translating relay corresponding to the length of the received signal impulse. Thus relay 9i is operated responsive to a .002 second impulse; relay 92 is operated responsive to a .004 second impulse; relay 93 is operated responsive to a .093 second impulse; relay 94 is operated responsive to a .016 second impulse; and relay 95 is operated responsive to a .032 second impulse. Each of relays 9|, 92, 93, 94 and 95 is slow in releasing due to the condenser and resistance associated there-- with. For instance condenser 8l associated with relay 9| discharges when relay 9i is operated and the charging of condenser 3l maintains the operation energization of relay 9i for about .l0-O second after its operating circuit is opened. Since both impulses of a signal consisting of the longest combination of signal impulses will be received within .100 second, the second impulse will effect the operation of a second one of relays 9|, 92, 93, 94 and 95 before the relay operated responsive to the rst impulse of a digit signal has released. With any two of relays 9|, 92, 93, 94 and 95 operated, a circuit is closed for operating the corresponding one of the digit signal devices i to 0. If only one of relays 9i, 92, 93, 94 and 95 is operated, none of the signal devices will be operated; and, if more than two of these relays are simultaneously operated, the marginal relay 99 is also operated. Relay 99 thereupon closes a circuit for operating a reorder signal whereby the calling station or operator will start the call over again.

While the impulses transmitted from station A are open circuit impulses, it is obvious that the arrangement may be modified so that the digit signal impulses constitute current impulses rather than open circuit impulses and further that the current impulses may be either alternating or direct current. These and other modications may be made within the scope of the invention as defined by the claims.

What is claimed is:

1. In a signaling system in which the transmission of each of a plurality of diiferent signals is effected by the same number of successive signal impulses, each impulse having a duration equal to a different one of a plurality of different predetermined intervals and each signal diifering from the others of said plurality in the duration of one or more of its impulses, a signaling circuit comprising a resistance and impulse transmitting contacts in series, a rst thermionic tube, the

control grid of said tube connected to said ref;

- sistance whereby the opening of said circuit by an impulse transmitting contact changes the po-;i tential of said grid with respect to the cathode of said tube, impulse measuring means compris-l ing a thermionic tube and a relay for each of said predetermined intervals of time, means comprising a second thermionic tube and said rst tube for operatively energizing said impulse measuring tubes in succession to measure the duration of a received impulse, a third thermionic tube and relay effective in combination with said first tube and said measuring tubes to operate one or more of the impulse measuring relays in accord. ance with the duration of the received impulse. translating relays one for each of said time measuring relays, means for operating the translating relay corresponding to the last operated one of said time measuring relays for each impulse, means for maintaining the translating relays operated for an interval sufcient for all of the impulses of a signal to have been received and the corresponding time measuring relays to have been operated, and signal means controlled by said translating relays to indicate the particular signal represented by the successive impulses constituting a signal.

2. In a signaling system in which the trans-I mission of each of a plurality of different signals is effected by the transmission of the same num--` ber of successive impulses in an electrical sig-J naling circuit, each impulse of a signal being of like character except that its length is equal to a different one of a plurality of different pre-v determined intervals of time, which plurality is larger than the number of impulses constituting each signal, each of said signals differing from the others in the length of one or more of its impulses, signal receiving means comprising impulse receiving means responsive to each impulse of any one of said different signals, impulse duration identifying relays, one relay for each of said different impulse lengths, for identifying the length of each signal impulse received by said impulse receiving means, means controlled by said impulse receiving means for operating one or more of said relays in succession responsive to each impulse of a signal in accordance with the length of the impulse, a plurality of selecting relays each corresponding to one of said duration identifying relays, means operated upon termination of each impulse for operating the selecting relay corresponding to the last operated duration identifying relay, means for maintaining the selecting relays operated for a predetermined time, and means operated by a combination of selecting relays for indicating the particular one of said signals which is received.

3. In a signaling system in which the transmission of each of a plurality of different signals is eifected by the transmission of the same number of successive impulses in an electrical signaling circuit, each impulse of the signal being of like character except that its length is equal to a different one of a plurality of different predetermined intervals of time, which plurality is larger than the number of impulses constituting each signal, cach of said signals differing from the others in the length of one or more of its impulses, signal receiving means comprising irnpulse receiving means responsive to each impulse of any one of said diiferent signals, impulse duration identifying relays, one relay for each of said diierent impulse lengths, for identifying the length of each signal impulse received by said amines 7 ixnpulse'receivingmeans,means :controlled bysaid impulse receiving means for operating -one or more of .said .relays :in succession .responsive to each impulse Vof :a .signal .in laccordance .with `:the length of the impulse, translating relays, onelfor each o1 said duration .identifying Ielaysymeans controlled `by said durationidentifying .relays and by means responsive to lthe Ytermination ,-of .each impulse for .operating :the :corresponding ztransl'ating` relay responsive:tofsuehimpulse cof. a signal, means .for maintaining the .operation vci" each operated translating relay .until fsuicient ,time has .elapsed for Vall Lui `tlieiinipulses.of .the signal to have been received, and signalzmeansselectively .operated-by the operationaof a: combination of said translating .relays ,responsive to the limpulses of .the signal :to .indicate .the signal :received.

4. In a .signaling systemin which the :transmission :of eachzcf alpluralityv of different signals is ei'ected byithetransrnission of .thesamenumbei' of .successive impulses, in. an` electrical signaling circuit,,eaenimpulseof asignalbeing of like characterexceptr that its .length .is equal: to. a.'different one oi" aplurality vof different predeter- .mined intervalsof time, whichplurality is larger than the number of impulses'constituting.each signal, each fof .said signals ydiffering from .the others in the length iof .one .ormore cf itsim pulses, .signal .receiving means comprisingsa first thermioni'c tube .responsive Ato .each :impulse .of each incoming. signal, .impulse :measuring means comprising therinionicltubes zoneltube. for. each; .of .said dierent impulse: lengths 'or measuring the .length 'of 'ea-eh `signal .impulse received l by zsai'd rirst tube, .impulsexduration identifying. relays, :a

8 relay for each impulse measuring tube, `means comprising said tubes for operating .one `or .more of said relays .depending .upon :the duration ,of each `impulse received by .said rst tube, theduration of .each v.impulse 'being .identied by .the last Vof said relays to .be operated responsive -rto the impulse, signal devices, one for eachiof said different signals, translating relays, means .controlledby said `duration identifying relays .and by means responsive to the termination of .each impulse yfoixoperazting vthe translating relay corresponding to :the last operated of fthe duration identifying relays lior each impulse of ,asignal .and means comprising a combination of trans,-

lating relaysfor eperating the signal device cor.- responding to any of said diierent signals lincoming to saidsignalireceiving means.

DOREN MITCHELL.

REFERENCES v,(.Il-"zED The vfollowing references are of record inthe le of this patenti UNITED STATES PATENTS 

